Garnets are capable of accommodating an excess of lithium cations beyond that normally found in this prototypical structure. This excess lithium is found in a mixture of coordination environments with considerable positional and occupational disorder and leads to ionic conductivity of up to 4 × 10⁻⁴ S cm⁻¹ at room temperature. This high value for total conductivity, combined with excellent thermal and (electro)chemical resistance makes these candidate materials for operation in all solid-state batteries. This review looks at garnets with a wide range of stoichiometries and lithium concentrations and the impact of complex lithium distributions and crystallographic order/disorder transitions on the transport properties of these materials.

The structure of the fast lithium-ion conducting garnets Li₅La₃M₂O₁₂ (M = Ta, Nb) reveals Li⁺ on both tetrahedral and octahedral sites and suggests that the latter are responsible for the observed Li⁺ mobility via a clustering mechanism.

The twelve-connected metal–organic frameworks {[Ni₃(OH)(L)₃]·n(solv)}_∞1 and {[Fe₃(O)(L)₃]·n(solv)}_∞2 [LH₂ = pyridine-3,5-bis(phenyl-4-carboxylic acid)] have been prepared and characterised: these materials can be desolvated to form porous materials that show adsorption of H₂ up to 4.15 wt% at 77 K.